Hydrogen has long been considered an ideal fuel source, as it offers a clean, non-polluting alternative to fossil fuels. One source of hydrogen is the splitting of water into hydrogen (H2) and oxygen (O2), as depicted in equation (1).2H2O→O2+2H2  (1)
In an electrochemical half-cell, the water-splitting reaction comprises two half-reactions:2H2O→O2+4H++4e−  (2)2H++2e−→H2  (3)and hydrogen made from water using sunlight prospectively offers an abundant, renewable, clean energy source. While the reduction of protons to form hydrogen is a relatively easy and efficient reaction, the oxygen evolution reaction requires a much higher driving force to overcome the activation energy barriers associated with the reaction as the reaction includes multiple proton coupled electron transfer processes. As such, efforts have been made to search for efficient water oxidation and oxygen evolution reaction (OER) catalysts that can produce oxygen and hydrogen ions from water. In particular, oxides of ruthenium and iridium have previously been identified. However, as they are among the rarest elements on earth, it is not practical to use these catalysts on a large scale. There is therefore a need for improved water oxidation and OER catalysts.